The Section works on elucidating the interaction of (complex) carbohydrate immuno-determinants with monoclonal antibodies (MAbs). Such interactions pertain to all ligand-protein interactions. We are executing: 1. Physico-chemical studies on antibody/antigen systems (Sh. dys. type 1, V. cholera). 2. The synthesis of ligands mimicking immunodeterminants of pathogenic entero-bacteria for affinity studies. 3. The study of immunodeterminants of these bacteria, so as to evaluate procedures for conjugate-vaccine development. 4. The amino acid sequencing by cDNA technique of monoclonal immunoglobulins obtained against pathogenic bacteria, and studies on the interaction of immunodeterminants with their energy minimized, tertiary structures. We are continuing to determine the specific interaction between microbial polysaccharides, and a number of monoclonal antibodies, such as Shigella dysenteriae type 1, Vibrio cholera and its monoclonal antibodies, and have prepared ligands to probe the fundamental nature of these antibody-antigen association. We have prepared additional complex fragments of the capsular polysaccharide of Shigella dysenteriae type 1 by sophisticated syntheses. These include deoxy and deoxyfluoro derivatives of the determinant. Studies are continuing on specific interactions between ligands and the binding area of a monoclonal antibodies specific for this disease-causing micro-organism. The amino acid sequence of some of these antibodies have been determined by cDNA cloning. Three dimensional antibody structures have been evaluated to delineate actual molecular forces involved in the binding.